Image processing method and apparatus

ABSTRACT

An image processing apparatus and method for processing color image signals. The apparatus comprises a first judgment unit for judging whether or not a pixel of interest belongs to a black line image portion, and outputting a first judgment signal indicating a judgment result, a second judgment unit for judging whether or not pixels in the vicinity of the pixel of interest belong to a black line image portion, and outputting a second judgment signal indicating a judgment result, and a control unit for controlling recording of the pixel of interest based on the first and second judgment signals outputted from the first and second judgment units. With the apparatus, black lines in a color image are satisfactorily reproduced.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an image processing apparatus,such as a color copying machine and a color FAX, for processing colorimage signals to record a color image using recording materials (such asink toners) of plural colors.

[0003] 2. Related Background Art

[0004] When color recording is performed by the additive color mixturebased on image signals obtained through color separation, it is generalthat black lines and characters, in particular, are recorded bysuperposing recording materials of three colors, i.e., Y, M and C, orfour colors, i.e., Y, M, C and K.

[0005] However, the superposition of recording materials of those threeor four colors raises the following problems:

[0006] (1) The resulting color by the superposition does not lookperfectly black,

[0007] (2) Difficulties in high-accurate superposition causes a colorshear or offset, which also makes the resulting color not look black,and

[0008] (3) In recording based on the pseudo-half-tone processing, therecording cannot be made by arraying dots in a continuous linear line.Thus, an image cannot be represented with high resolution. Meanwhile,the applicant has previously proposed in U.S. patent application Ser.No. 378,488, a method of representing a monochromatic image bydiscriminating and separating portions of lines and characters in animage from other image portions of half tone, and recording only theformer portions with high resolution, thereby allowing both gradationand resolution of the image to stand together in representation.

[0009] Although this method can solve the above problem (3), it has ashortcoming to require independent hardwares for different colors whenapplied to processing of a color image. Further, a method ofdiscriminating a black portion from color signals and judging a regionwhich coincides with a character portion extracted from the component ofone color, e.g., the G component, as a black character region stillaccompanies the problems that the black portion is difficult todiscriminate inexpensively with high accuracy, and that the judged blackregion is not always precisely coincident with the actual black region.In addition, the so-called black signal produced by masking or UCRcannot be employed for this type processing because that black signal isadapted to correct only black portions which can be represented by usingC, M and Y, and thus has not a sufficient level for line portions ofblack characters, in particular. To solve the above problems, theapplicant has previously proposed U.S. patent application Ser. No.173,654, U.S. Pat. No. 4,958,219, U.S. patent application Ser. No.327,098, U.S. patent application Ser. No. 367,673, and U.S. patentapplication Ser. No. 519,500, but there still remains room forimprovement.

[0010] Furthermore, it is conventional in image processing apparatusthat a color image is subjected to color separation into three colors,i.e., R, G and B, and C, M, Y and K (black) signals are then produced asrecord colors, followed by the pseudo-half-tone processing for each ofthe four colors. As a pseudo-half-tone processing technique, while thereis known for many years a dither method which can be constitutedinexpensively, a data storage type technique represented by an errordispersing method has become more popular in recent years which carriesout error correction through re-quantization for enabling resolution andgradation to be reproduced in a substantially compatible manner.

[0011] In the above pseudo-half-tone processing technique of datastorage type (i.e., the conditioned dither method), however,re-quantized dots are not directly determined from input data of onepoint. For the reason, when input image data obtained through colorseparation into four colors are processed independently, there-quantized dots in four colors may locally overlap with each other.Accordingly, in the case that recording is made using the electrostaticprocess based on the re-quantized data, for example, toners of fourcolors locally overlap with each other to form a projection with theheight of several 100 microns on the sheet surface of transfer paper,resulting in drawbacks of lowering a fixing property and degrading animage quality.

[0012] In the case of recording an image by an ink jet technique, forexample, a large amount of ink is jetted into a local area. This resultsin similar drawbacks that an ink smear occurs on the rear side ofrecording paper and a longer period of time is required for drying.

[0013] In addition, when deposit positions of recording materials ofdifferent colors are not perfectly coincident with each other for eachpixel by virtue of limitations in mechanical accuracy, a color shear iscaused and color reproducibility is badly deteriorated.

SUMMARY OF THE INVENTION

[0014] The present invention has been accomplished in view of theproblems as stated above, and has for its object to provide an imageprocessing apparatus which can satisfactorily reproduce a color image,particularly, a black color line in the color image.

[0015] To achieve the above object, the present invention discloses animage processing apparatus comprising first judgment means for judgingwhether or not a pixel of interest belongs to a black line imageportion, and outputting a first judgment signal indicating a judgmentresult, second judgment means for judging whether or not pixels in thevicinity of said pixel of interest belong to a black line image portion,and outputting a second judgment signal indicating a judgment result,and control means for controlling recording of said pixel of interestbased on the first and second judgment signals outputted from said firstand second judgment means.

[0016] Also, there is disclosed an image processing method comprising afirst judgment step of judging whether or not a pixel of interestbelongs to a black line image portion, a second judgment step of judgingwhether or not pixels in the vicinity of said pixel of interest belongto a black line image portion, and a control step of controllingrecording of said pixel of interest based on judgment results in saidfirst and second judgment steps.

[0017] Another object of the present invention is to provide an imageprocessing apparatus which has a simplified circuit configuration.

[0018] To achieve that object, the present invention discloses an imageprocessing apparatus comprising m-value coding means for coding aplurality of color component signals, each in n bits, one by one intoany value ranging from 0 to m (where 2<m<n), judgment means for judgingwhether or not an image represented by said plurality of color componentsignals belongs to a black line image portion, and control means forcontrolling, based on a judgment result by said judgment means,recording with a plurality of color component signals which have beencoded by said m-value coding means into any value ranging 0 to m.

[0019] Still another object of the present invention is to provide animage processing apparatus suitable for high-speed processing andreal-time processing.

[0020] To achieve that object, the present invention discloses an imageprocessing apparatus comprising means for binary-coding a plurality ofcolor component signals color by color, means for removing minor colorcomponents from said color component signals, and means for generatingrecord color signals by using both the color component signal left afterremoving said minor color components and said color component signalsbefore the binary-coding.

[0021] Yet another object of the present invention is to provide animage processing apparatus which has satisfactory color reproducibility.

[0022] To achieve that object, the present invention discloses an imageprocessing apparatus comprising detecting means for detecting a blackline image portion in an input color image, and generating means forgenerating record signals to record the black line image portion,detected by said detecting means, by superposing multiple dots includinga black dot.

[0023] Also, there is disclosed an image processing method comprisingthe steps of detecting a black line image portion in an input colorimage, and generating record signals to record said black line imageportion by superposing multiple dots including a black dot.

[0024] Other objects and modes of the present invention will be apparentfrom the following explanation with reference to the attached drawingsand the description of claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025]FIGS. 1A to 1C are views showing an entire configuration of afirst embodiment of the present invention,

[0026]FIGS. 2A to 2D are views for explaining generation of a blacksignal,

[0027]FIG. 3 is a view showing a binarization unit,

[0028]FIG. 4 is a view showing a black character discrimination unit,

[0029]FIG. 5 is a view showing a circuit for judging a screen pixel,

[0030]FIG. 6 is a view showing a black character signal generation unit,

[0031]FIG. 7 is a view showing a record signal control unit,

[0032]FIGS. 8A to 8C and FIGS. 9A to 9D are views for explaining amodification of the first embodiment of the present invention,

[0033]FIGS. 10, 11 and 12 are views for explaining a record apparatus(element),

[0034]FIG. 13 is a view showing an entire configuration of a secondembodiment of the present invention,

[0035]FIG. 14 is a view for explaining generation of a black signal,

[0036]FIG. 15 is a view showing a binarization unit,

[0037]FIG. 16 is a view showing a black character discrimination unit,

[0038]FIGS. 17 and 18 are views for explaining a modification of thesecond embodiment of the present invention,

[0039]FIGS. 19 and 20 are views showing an entire configuration of athird embodiment of the present invention,

[0040]FIG. 21 is a view showing a binarization unit 360,

[0041]FIG. 22 is a view for explaining a manner of the binarization,

[0042]FIG. 23 is a view showing a configuration of an error correctionunit 304,

[0043]FIG. 24 is a view showing a YMC color space, and

[0044]FIGS. 25, 26, 27 and 28 are views for explaining a modification ofthe third embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0045] [First Embodiment]

[0046]FIG. 1A is a block diagram showing an entire configuration of afirst embodiment of the present invention. In the drawing, designated byreference numeral 1 is a color CCD line sensor which performs colorseparation substantially at the same point on an original document intosignals in three colors R, G and B, and also quantizes each color signalusing 8 bits. The R, G and B signals point-sequentially read by thesensor 1 are inputted to a color processing unit 2 for the so-calledcolor signal processing such as log conversion, masking, UCR and gamma(γ) conversion, thereby obtaining 8-bit record signals in record colorsof Y, M, C and K. These record signals are subjected to the so-calledpseudo-half-tone processing, for example, an error dispersing method ora mean density storage method, in respective binarization units 3-1,3-2, 3-3 and 3-4. On the other hand, the R, G and B signals resultedfrom color separation are also inputted to a black signal generationunit 6, which is a feature of the present invention, to produce a blacksignal d having 8 bits, i.e., 256 levels, and being suppressed in acolor tint. The black signal d is binary-coded by a binarization unit 7with high accuracy. A resulting binary signal is inputted to a blackcharacter discrimination unit 8 which discriminates and separatescharacter/line image portions from half-tone image portions and screenimage portions, followed by applying a signal indicative of thediscrimination result to a record signal control unit 4. The controlunit 4 controls, based on the discrimination signal, the aforesaidbinary signals in four colors which have been binary-coded independentlyof one another, thereby driving record element (apparatus) 5 to make arecording.

[0047] The first embodiment of the present invention will now bedescribed in detail in the order of the black signal generation unit 6,the binarization unit 7, the discrimination unit 8, and the binary datacontrol unit 4. It is to be noted that the color signal processing unit2 and the binarization unit 3 can be constituted by totally adopting thewell-known technology and, therefore, will not be explained here.

[0048] <Black Signal Generation Unit>

[0049]FIG. 2A shows the black signal generation unit 6. In the drawing,a max value detection unit 61 and a min value detection unit 62 eachcompare levels of the RGB signals, each represented by 8 bits, with eachother per pixel and respectively obtain a value having the highest leveland a value having the lowest level as max(RGB) and min(RGB). An adder63 calculates a difference between the obtained two signals, i.e.,max(RGB)−min(RGB), The calculated result is multiplied by a presetconstant α in a multiplier 66, and the product is added to the max(RGB)in an adder 64. The added result is limited to 255 by a limiter 65 whenit exceeds the 8-bit width, for producing the black signal d.

[0050]FIG. 2B shows an explanatory view for that processing. It isassumed in this embodiment that as the color signals R, G and B havelarger values, the pixel color approaches white and becomes black whenR=G=B=0 holds. In FIG. 2B, therefore, a region A represents a line witha color tint and a region B represents a black line.

[0051] The calculation executed in the black signal generation unit 6 isexpressed by the following equation (1):

d=max(RGB)+α[max(RGB)−min(RGB)]  (1)

[0052] (where max(RGB) is a gray component signal, max(RGB)−min(RGB) isa signal indicating a color tint, and α is a color suppression constant)

[0053] This processing has a physical meaning as follows. Assuming nowthat max(RGB)−min(RGB) indicates a color tint and max(RGB) indicates agray component (brightness), it is possible, when max(RGB)−min(RGB) islarge, i.e., for a pixel having a color tint, to perform conversion in adirection to increase brightness (white level) by multiplying thedifference value by the constant α and adding the product to max(RGB).Accordingly, the larger the value of the constant α, the closer thepixel having a color tint approaches a white level. Thus, a is called acolor suppression constant of which value represents a degree ofsuppressing a color tint. Stated otherwise, by making a not-shown CPUchange the value of a to be set by the multiplier 66, the degree ofdetection of a black component indicated by d can be varied. The valueof a may be, for example, set by an operator from a not-shown console.Even in the case of α=1 shown in FIG. 2B, if max(RGB) is large and so ismax(RGB)−min(RGB), the pixel of interest takes the maximum value of 255representing a perfect white level by operation of the limiter 65 inFIG. 2A. Consequently, it is believed that changes in the producedsignal d nearly implies changes in the black component.

[0054] The black signal d is inputted to the binarization unit 7 shownin FIG. 3.

[0055] <Binarization Unit>

[0056] In FIG. 3, data of the black signal d are delayed and held byusing memories 71 on a line by line basis, and the data of five pixelsthus successively delayed are added in an adder 72. The added value forevery five pixels is applied to flip-flops (F/F's) 73 to be successivelydelayed and held on a pixel by pixel basis, and the resulting five addedvalues are further added in an adder 75. Assuming that the position ofan output of an F/F 73-6 resulted from delaying an output of the memory71-2, which is resulted from delaying the input data by two lines, bytwo pixels through F/F's 73-5 and 73-6 is a position of the pixel ofinterest, an output of the adder 75 is an integral value of pixelssurrounding the pixel of interest. Accordingly, a mean value m of theblack signals in the vicinity of the pixel of interest is obtained bydividing the integral value in a divider 76.

[0057] A comparator 79 compares the data d about the position of thepixel of interest with a threshold given by the mean value m, therebyobtaining a more accurate binary signal B. Specifically, the comparator79 produces an output in accordance with the following rules:$\left\{ {\begin{matrix}{{{{If}\quad d} < m},{{{then}\quad B} = {1\quad ({black})}}} \\{{{{If}\quad d} \geqq m},{{{then}\quad B} = {0\quad ({white})}}}\end{matrix}\quad} \right.$

[0058] Furthermore, the difference between both the average values m andd is determined by an adder 77 and converted into an absolute value byan absolute value circuit 78. Then, the absolute value is compared witha constant δ in a comparator 74 to obtain a binary signal C inaccordance with the following rules: $\left\{ {\begin{matrix}{\left. {If}\quad \middle| {d - m} \middle| {> \delta} \right.,{{{then}\quad C} = 1}} \\{\left. {If}\quad \middle| {d - m} \middle| {\leqq \delta} \right.,{{{then}\quad C} = 0}}\end{matrix}\quad} \right.$

[0059] The above two signals have physical meanings that the formersignal B is a signal resulted from high-accurately binarizing the blacksignal, whereas the latter signal C is a signal resulted from binarizinga level change amount at the pixel of interest. Specifically, in thecase of B=1 5 and C=1, it can be judged that the density change at thepixel of interest is larger than the constant δ and shifted toward ablack level. Thus, the probability that the pixel of interest is a partof character lines can be said high.

[0060] However, the pixel of interest may possibly belong to a half-toneimage portion expressed by a screen. To eliminate the possibility of ascreen, therefore, signals of 2 bits, i.e., signals B, C, are inputtedto the black character discrimination unit 8 for discriminating acharacter image portion.

[0061] <Black Character Discrimination Unit>

[0062]FIG. 4 shows the black character discrimination unit. First, thebinary signal B inputted thereto is successively delayed and held byusing line memories 80-1, 80-2, 80-3, 80-4 on a line by line basis, andalso successively delayed and held by flip-flops (F/F's) 81-1 to 81-9 ona pixel by pixel basis. Accordingly, assuming now that the position ofthe pixel of interest is an output position of the F/F 81-4, the binarydata B of 8 pixels adjacent the pixel of interest are obtained at inputterminals of the F/F's 81-2, 81-4, 81-6 and output terminals of theF/F's 81-2, 81-6, 81-3, 81-5, 81-7. Then, the adjacent nine pixel dataincluding the pixel of interest are all inputted to a gate circuit 83-2.

[0063] Considering in a like manner, pixel data one line after the abovepixel of interest, i.e., data of 9 pixels adjacent the output positionof the F/F 81-2, are inputted to a gate circuit 83-1, and pixel data oneline before the above pixel of interest, i.e., data of 9 pixels adjacentthe output position of the F/F 81-6, are inputted to a gate circuit83-4. In each gate circuit 83 (though described later in detail),depending on whether or not the binary level (0 or 1) of the centralpixel is inverted from the binary levels of the adjacent eight pixels,i.e., whether or not the central pixel has a level of “0” or “1”isolatedly from the surrounding pixels, a value S ranging from 0 to 4 isassigned to each pixel. It can be said that the larger the value S, thehigher the probability that the pixel of interest belongs to a screenimage portion and, conversely, the value S of 0 means the higherprobability that the pixel of interest belongs to a character or likeline. This is because that a character line is given by a set ofone-dimensionally continuous dots. But, since whether or not the pixelof interest is a part of characters cannot be judged from one pixel,this judgment is made by two-dimensionally integrating the value S whichis assigned to each pixel and represents a degree of isolation. In otherwords, multi-value data indicating a degree of isolation is used in thejudgment. First, the data of 3 pixels in the direction of line are addedin an adder 85-1, and the added result is successively delayed and heldover six pixels by F/F's 84-1 to 84-6. Then, the respective delayed dataare added, along with the current data, in an adder 85-2 to obtain anadded value Pf of the data S for 3×7 pixels about the pixel of intereston the assumption that the pixel delayed from the input image data B by2 lines and 4 pixels gives a position of the pixel of interest. Thisfeature amount Pf implies two-dimensional spatial frequency. In short,the larger value Pf means that the more binary data B are inverted intheir values between “0” and “1” in the vicinity of the pixel ofinterest, i.e., the spatial frequency is higher, and thus there are moretwo-dimensionally isolated dots. The value Pf is processed in accordancewith the following rules: $\left\{ {\begin{matrix}{\quad {{{{If}\quad {Pf}} > K},{C = {{1\quad {and}\quad B} = 1}},{{{then}\quad E} = 1}}} \\{\quad {{{If}\quad {otherwise}},{{{then}\quad E} = 0}}}\end{matrix}\quad} \right.$

[0064] More specifically, the value Pf is compared with a presetconstant K (on the order of 4 to 5) in a comparator 86. A signal Dindicating the compared result, the binary signal C at the position ofthe pixel of interest, i.e., the signal resulted from delaying the inputimage data by 2 lines through memories 80-5, 80-6 and by 4 pixelsthrough F/F's 82-1 to 82-4, and the binary signal B at the same positionare ANDed by an AND circuit 87. Letting an output value of the ANDcircuit 87 be E, E=1 indicates that the pixel of interest is a part ofblack characters.

[0065] The signal E and the signal B which is delayed from the positionof the pixel of interest by 1 line and by 2 pixels through F/F's 89-1,89-2 are inputted to a black character signal generation unit 88 toproduce black character signals KB and KW as final outputs.

[0066] The internal configuration of the gate circuit 83 will now beexplained in more detail. FIG. 5 is a block diagram showing the gatecircuit 83 in which a, b, c, d, e, f, g and h adjacent a central pixel icorrespond to respective input and output signals B of the F/F's 81.EX-OR gates 831-1, 831-2 and an AND gate 832-1 serve to detect whetheror not a level of the pixel i of interest is inverted in a directionpassing the pixels a, i and h. Specifically, if outputs of the EX-ORgates are both “1”, then the AND gate 832-1 produces an output of “1”,meaning that the pixel i of interest is isolated in the direction of(aih). Likewise, EX-OR gates 831-3, 831-4 and an AND gate 832-2 serve todetect isolation of the pixel i of interest in a direction of (cif),EX-OR gates 831-5, 831-6 and an AND gate 832-3 serve to detect isolationthereof in a direction of (big), and further EX-OR gates 831-7, 831-8and an AND gate 832-4 serve to detect isolation thereof in a directionof (die). Then, AND gates 833-1, 833-2 and an OR gate 834 serve todetect the case that the pixel i of interest is at the same level “0” or“1” continuously in the direction of (big) or (die). If so, an output ofthe OR gate 834 becomes “0”. This output signal is ANDed in AND gates835-1 to 835-4 with each of outputs of the AND gates 832-1 to 832-4, andthe output results are added in an adder 836 to determine the value Sindicating any one of 0 to 4.

[0067] The conditions provided by the AND gates 833 and the OR gate 834have a physical meaning as follows. Since the continuity in thedirection of (big) or (die) indicates one of segments of linesorthogonal to each other on a paper sheet (i.e., the original documentor recording paper), the probability that the pixel of interest is apart of characters is high. In this case, therefore, S=0 is exclusivelyset to reduce the feature amount Pf.

[0068] In order to execute the above detection algorithm of segments oflines with higher accuracy, it is desirable that the setting of S=0 islimited to the case where the pixels b, i, g are all 0 (or 1) and a, d,f, c, e, h are all 1 (or 0), or where the pixels d, i, e are all 0(or 1) and a, b, c, f, g, h are all 0 (or 1). Further, detecting a slantline and setting S=0 can be easily implemented in a like manner byadding circuits like the AND gates 833 and the OR gate 834 so as todetect the case where the pixels c, i, f are all 0 (or 1) and the othersare all 1 (or 0), or where the pixels a, i, h are all 0 (or 1) and theothers are all 0 (or 1).

[0069] It is also desirable for higher accurate discrimination ofcharacters that an area over which data are integrated to obtain thevalue Pf is square and larger on the order of 7×7 than the illustratedembodiment. Note that the block size and the block shape are not limitedto the above embodiment, and may be optionally set depending ondetection accuracy or other factors.

[0070] Next, the internal configuration of the black character signalgeneration unit 88 will be described by referring to FIG. 6. This unit88 is to produce a signal KB (1 bit) indicating that the pixel ofinterest is a part of black characters when KB=1 holds, and a signal KW(1 bit), i.e., a black character adjacent pixel position signal,indicating that the pixel of interest is adjacent the black characterimage portion, but does not itself belong to the black character imageportion (i.e., B=0) when KW=1 holds. More specifically, the unit 88receives the 1-bit signals E and B, the signal E being delayed on a lineby line basis through memories 80-7 and 80-8 (FIG. 5). The signals E arefurther delayed on a pixel by pixel basis through F/F's 880-1 to 880-5so that letting the position of the pixel of interest be an outputposition of the F/F 880-3, an OR gate 881 produces an output of “1” whenany one of 8 pixels adjacent the pixel of interest exhibits E=1.Accordingly, when the signal B is delayed by an F/F 880-7 to be matchedwith the position of the pixel of interest, inverted in its level andinputted to an AND gate 882, the signal KW signal is obtained. Thesignals KB and KW are applied to the control signal control unit 4 as afeature of this embodiment for controlling the record signals. Thecontrol signal control unit 4 will be explained below in detail.

[0071] <Control Signal Control Unit 4>

[0072] Since the internal processing is delayed by 5 lines and severalpixels with respect to the binary data because of the above generationof the black character signals KW, KB, the binary data are delayed to bematched with the position of the signals KB and KW. Memories 40-1 to40-4 in FIG. 7 constitute respective delay circuits for that purpose, tothereby control binary record signals 2C, 2Y, 2M and 2K as follows:

[0073] If KB=1, $\left( {\begin{matrix}{\quad {{{then}\quad K} = {1\quad \ldots \quad a\quad {dot}\quad {is}\quad {recorded}}}} \\{\quad {{{then}\quad C},M,{Y = {0\quad \ldots \quad {dots}\quad {are}\quad {not}\quad {recorded}}}}}\end{matrix}\quad} \right.$

[0074] If KW=1, then C, M, Y=0

[0075] Thus, the black record signal records a dot based on the resultof logical sum (OR) of the signal 2K and KB=1, and also stops andsuppresses color recording to avoid color mixing the color record signalis present at the same position. For those pixel producing the signalKW=1, the color record signal is likewise suppressed to stop recordingof a dot in the vicinity of a black character for clearer recording.

[0076] The relationships between KB, 2K, KW and dot recording are listedin Table 1 below. TABLE 1 (KB, 2K, KW) Dot Recording (1, 1, 1) K = 1, C= M = Y = 0 (1, 1, 0) K = 1, C = M = Y = 0 (1, 0, 1) K = 1, C = M = Y =0 (1, 0, 0) K = 1, C = M = Y = 0 (0, 1, 1) K = 1, C = M = Y = 0 (0, 1,0) K = 1, C = M = Y = 0 (0, 0, 1) K = 0, C = M = Y = 0 (0, 0, 0) K = 0,For C, M and Y, usual binary data are recorded

[0077] <Record Apparatus 5>

[0078] The configuration of the record apparatus 5 in FIG. 1A will benext described.

[0079] The present invention is applicable to various recordingtechniques such as ink jet recording, thermal transfer recording,electrostatic recording and electrophotographic recording. The followingis an explanation relating to an example in which the present inventionis applied to ink jet recording.

[0080]FIG. 10 is a perspective view of a head and thereabout of an inkjet recording apparatus which uses heat generating elements.

[0081] In the drawing, designated at 51 is a head unit having total fournozzles 52. More specifically, the head unit 51 has a black inkdischarge nozzle 52K, an yellow ink discharge nozzle 52Y, a magenta inkdischarge nozzle 52M, and a cyan ink discharge nozzle 52C. 53 is an inksupply tube and 54 is a main tank which is provided four in numbercorresponding to the nozzles one to one relation.

[0082] The structure of each nozzle 52 will now be explained byreferring to a sectional view of FIG. 11. Designated by 55 is an upperplate, 56 a bottom plate, 57 a heat generating element, 58 an orifice,and 59 ink.

[0083] Upon application of voltage, the heat generating element 57produces heat to create bubbles in the vicinity thereof, and upon theend of voltage application, the bubbles are contracted. In response tothe formation and contraction of the air bubbles, the ink near theorifice 58 is discharged from the orifice 58.

[0084] The above-stated recording head is one of so-called bubble jettype that the ink causes a state change such as film boiling underthermal energy for producing bubbles, and is jetted with the aid of thebubbles from the discharge port (nozzle) toward material on whichrecording is to be made, thereby recording characters, pictures and thelike. With this type recording head, the size of the heat generatingresistor (heater) provided in each nozzle is much smaller than apiezoelectric element used in conventional ink jet recording. Thisenables installment of the nozzles with higher density and imagerecording with higher quality, resulting in a benefit of high-speed andlow-noise operation.

[0085] Moreover, a record apparatus may be used which has a multiplicityof heads for one kind of coloring material.

[0086] In FIG. 12, designated by 101 is a head unit in which amultiplicity of ink jet heads are arranged for one kind of coloringmaterial in the sub-scan direction, the head unit being provided foreach of black, yellow, cyan and magenta. 107 is an ink tank for the headunit, 109 is a signal line, and 104 is a carriage drive motor for movinga carriage 105 along a pair of rails 103 in cooperation with a conveyorbelt 102, with the head unit being mounted to the carriage 105. 106 isrecording paper, 120 is a platen, 111, 112 are rollers for feeding therecording paper, 113 a roll of the recording paper, and 114 is a guideroller. While the head unit 101 comprises a plurality of ink jet headseach utilizing the heat generating element shown in FIG. 11, it may ofcourse employ ink jet heads using piezoelectric elements orelectro-mechanical transducer means, for example.

[0087] <Another Embodiment (1) of Black Signal Generation Unit 6>

[0088]FIG. 2C shows another embodiment (1) of generation of the blacksignal. In the foregoing embodiment, the color tint suppression constantis given by the constant value a regardless of the gray componentmax(RGB). Generally, however, the larger the gray component, i.e., thebrighter the pixel of interest, the more frequently the pixel ofinterest has a color tint. In view of that, as the pixel of interest isbrighter, the degree of suppressing a color tint is made larger in thisembodiment. By so setting, there can be produced the black signal d withhigher contrast. An equation for calculating this type black signal d isbelow:$d = {{\max \left( {R\quad G\quad B} \right)} + {\frac{\max \left( {R\quad G\quad B} \right)}{\beta}\left\{ {{\max ({RGB})} - {\min ({RGB})}} \right\}}}$

[0089] The value of max(RGB)−min(RGB) obtained from the adder 63 ismultiplied by the output max(RGB) of the max detection unit in amultiplier, and the multiplied result is divided by a constant β in adivider 662. The value of β is preferably about 128, for example. Thedivided result is added to max(RGB) in the adder 64, followed byclamping by the limiter 65 to 255.

[0090] <Another Embodiment (2) of Black Signal Generation Unit 6>

[0091] While a color tint is defined by the difference between max(RGB)and min(RGB) in the above embodiment (1) and suppressed through theadding operation, the color tint may be defined by a ratio of max(RGB)to min(RGB) and suppressed through a multiplying operation of max(RGB).This operation is expressed below:$d = {{\max \left( {R\quad G\quad B} \right)} \times \frac{\max \left( {R\quad G\quad B} \right)}{{\min ({RGB})} + \gamma}}$

[0092] Here, the value of a constant γ is preferably about 63. From theabove equation, it will be found that the larger the gray component,i.e., the brighter the pixel of interest, the more effective thesuppression of the color tint, and that the degree of suppression isalleviated depending on the constant γ in some region, i.e., whenmax(RGB) and min(RGB) are both small. Therefore, even when the pixel ofinterest has a color tint in addition to the black component, the valueof d will not be increased to enable generation of the black signal dwith improved contrast. In this embodiment shown in FIG. 2D, the outputof the min detection unit 62 is first added to the constant γ in anadder 663, and the added result is divided by the output of the maxdetection unit 61 in a divider 664. Then, the divided result ismultiplied by max(RGB) in a multiplier 665.

[0093] Although the algorithm of producing multi-value data, suppressedin a color tint, from the R, G and B data has been explained above, itis a matter of course that the present invention is not limited to thatalgorithm, particularly, to the use of primary colors RGB, and thesimilar operating effect can be also obtained by using other colorcomponent signals such as record colors YMC, for example.

[0094] <Another Embodiment (1) of Record Data Control Unit 4>

[0095] While the foregoing embodiment has been disclosed as controllingthe record data after binarization, another embodiment of controllingmulti-value data before binarization will be described by referring toFIGS. 1B and 8.

[0096] In FIG. 1B, the data converted by the color signal processingunit 2 into the four color signals of C, M, Y and K are controlled bythe signals KW, KB of 2 bits outputted from the black charactergeneration unit 8, and then binary-coded in the binarization unit 3,followed by recording. In the case of employing this embodiment, whenthe record element 5 is a laser beam printer in which the dot size canbe modulated in multi-stages by the pulse width modulation or brightnessmodulation, or is a thermal record element such as a piezoelectric typeink jet printer or thermal transfer printer in which dots can berecorded in variable tones, the binarization unit 3 is not alwaysrequired and the controlled multi-value data may be directly recorded.

[0097] The internal configuration of a record signal control unit 9according to this embodiment will now be explained in detail byreferring to FIG. 8. In FIG. 8A, memories 91, 92, 93 and 94 constituterespective delay circuits for matching in position with the blackcharacter signals KW, KB like the foregoing embodiment. Then, themulti-value data in the respective colors are directly converted on apixel by pixel basis depending on KB and KW through LUT (Look-Up Table)using ROM's 95, 96, 97 and 98.

[0098] In the case of KB=1, a γ table is selected and used for thelook-up which enhances the input data toward a black level as shown inFIG. 8C for the black signal K, and enhances the input data toward awhile level conversely as shown in FIG. 8B for the color signals C, Mand Y.

[0099] In the case of KW=1, the degree of enhancement for the colorsignals C, M and Y is slightly alleviated as compared with the case ofKB=1. With this embodiment designed to control multi-value levels, sincethe surroundings of a black character having a background color can becontrolled to a light color in a natural extent, particularly, in thecase of KW=1, a record image can be obtained with higher quality.

[0100] It is needless to say that in the case of KB=1, CK=255 and CM,CC, CY=0 may be set regardless of the input data. In addition, the LUTmay be performed using RAM's.

[0101] <Another Embodiment (2) of Record Data Control Unit 4>

[0102] While the foregoing embodiments have been described as executingthe black character-processing after masking and UCR, the primary colorsignals, i.e., the R, G and B signals may be directly controlled, asshown in FIG. 1C, with the similar operating effect. A record datacontrol unit 10 of this embodiment shown in FIG. 1C will now beexplained in detail by referring to FIG. 9.

[0103] In FIG. 9A, delay memories 101, 102 and 103 used like the aboveembodiment are each a memory having the same capacity as the memories91, 92, 93 and 94 in the embodiment shown in FIG. 8A. But, since amemory for one color can be dispensed with in this embodiment, therecord data control unit 10 can be realized with simple construction.The input data of respective colors are converted through LUT conversionusing ROM's 104, 105 and 106.

[0104] The respective color signals are enhanced toward a white level inthe case of KW=1 as shown in FIG. 9C and, conversely, enhanced toward ablack level in the case of KB=1 as shown in FIG. 9D. By subjecting thethus-converted data to usual masking and UCR, the signals Y, M, C and Kare all enhanced toward a white level in the case of KW=1. On thecontrary, in the case of KB=1, the signal K is enhanced toward a blacklevel, while the signals C, M and Y are enhanced toward a white level.Note that conversion characteristics are not limited to linear ones inthe above two embodiments, and use of non-linear characteristics makesit possible to control the input signal so as to become more black inthe case of KB=1, and the color signals so as to become more white inthe case of KW=1.

[0105] As described above, the foregoing embodiments have the followingadvantages:

[0106] (1) Black characters and lines in an image can be discriminatedinexpensively with high accuracy, enabling characters to be recorded bythe use of a single black color with high resolution,

[0107] (2) Even if a color shear is caused during the recording, blackcharacters can be clearly recorded in black, and

[0108] (3) Particularly, according to the foregoing embodiments, sincethe black color signal is extracted and the line and half-tone imageportions are discriminated based on the extracted black signal, there isno need of newly generating a black signal for the purpose ofdiscrimination, which can lead to simplification of the circuitconfiguration.

[0109] As printers to output the record signals generated in anabove-stated manner, there can be used such printers capable of colorrecording as a color ink jet printer, a color thermal transfer printer,a color dot printer and a color laser beam printer.

[0110] In particular, the present invention represented by the foregoingembodiments is effective for use in a printer having a head of the typethat droplets are discharged by utilization of film boiling underthermal energy, as disclosed in U.S. Pat. Nos. 4,723,129 and 4,740,793.

[0111] The aforementioned arithmetic circuits may be constituted usingROM's, RAM's or the like, or may be realized by a software executed in acomputer to implement the above arithmetic operations.

[0112] Other than being applied from the CCD sensor, the image data maybe applied from a host computer through an interface, or from anexternal memory.

[0113] According to the foregoing embodiments of the present invention,as explained above, black lines in a color image can be satisfactorilyreproduced.

[0114] [Second Embodiment]

[0115]FIG. 13 shows a block diagram of a second embodiment of thepresent invention. In the drawing, designated by reference numeral 201is a CCD line sensor for reading a color image, which readssubstantially the same point on an original document through colorseparation into signals in three colors R, G and B, and also quantizeseach color signal using 8 bits. Outputs of the sensor 201 are convertedinto 8-bit record signals in record colors of Y, M, C and K in a colorsignal processing unit 2 by the so-called color signal processing suchas log conversion, masking, UCR and gamma (r) conversion.

[0116] On the other hand, the R, G and B signals are inputted to a colorjudgment unit 206, which is a feature of the present invention, toproduce a 1-bit judgment signal d indicating black or not on a pixel bypixel basis. Also, the G signal is binary-coded by a binarization unit207, which is also a feature of the present invention, with highresolution. Based on a resulting binary signal and the black judgmentsignal d, a black character discrimination unit 208 produces a 1-bitsignal KB indicating a black character image portion and a 1-bit signalKW indicating a pixel adjacent the black character image portion. In arecord signal control unit 204, the black character signals KB, KW of 2bits control the C, M, Y and K signals each having a 8-bit width andoutputted from the color signal processing unit 202. More specifically,for a black character image portion, the signal K is enhanced, but theC, M and Y signals are suppressed. Therefore, as the result ofsubjecting those data to pseudo-half-tone processing in respectivebinarization units 203 independently, a clear image can be recorded by arecord apparatus 205 while representing the black character and lineimage portions by the use of black dots only. Since the presentinvention is featured by the color judgment 206, the binarization unit207, the black character discrimination unit 208 and the record signalcontrol unit 204 as mentioned above, detailed description of othercomponents are omitted and those units will be explained below one byone.

[0117] <Color Judgment Unit 206>

[0118]FIG. 14 shows the color judgment unit 206 for making a judgment ofblack or not based on the R, G and B signals, and producing the blackjudgment signal d. In the drawing, a max detection unit 260 and a mindetection unit 261 are blocks to determine a maximum value max(RGB) anda minimum value min(RGB) in the R, G and B signals inputted for eachpixel, respectively. When the max and mini values are both 255 (or 0),the pixel of interest is white (or black). A judgment algorithm in thisembodiment is expressed by: $\begin{matrix}\left. \begin{matrix}{\quad {{{\max \left( {R\quad G\quad B} \right)} - {2{\min \left( {R\quad G\quad B} \right)}}} < {K\quad a}}} \\{\quad {{{\max \left( {R\quad G\quad B} \right)} - {\min \left( {R\quad G\quad B} \right)}} < {K\quad b}}} \\{\quad {{{\max \left( {R\quad G\quad B} \right)} - {{1/2}\quad {\min \left( {R\quad G\quad B} \right)}}} < {K\quad c}}} \\{\quad {{\max \left( {R\quad G\quad B} \right)} < {K\quad d}}}\end{matrix} \right\} & (1)\end{matrix}$

[0119] If the above conditions (1) are all met, then the pixel ofinterest is judged as black (d=0). Thus, the results of comparison madein comparators 266-1, 266-2, 266-3 and 266-4 with respective constantsKa, Kb, Kc and Kd are inputted to a NAND gate 262 to obtain the judgmentresult d. Incidentally, a delay memory 263 is one necessary for timingadjustment with respect to the black character discrimination unit 208.In this embodiment, the values of the constants are assumed to be Ka=16,Kb=32, Kc=96 and Kd=160.

[0120] <Binarization Unit 207>

[0121]FIG. 15 is a block diagram of the binarization for judging blackcharacters. In this embodiment, the G signal is binary-coded to detectblack characters by using the G signal alone among the three R, G and Bsignals. A threshold for binarization is assumed to be a mean valueobtained by simply adding data in an area of 5×5 adjacent the pixel ofinterest, and the difference between the binary-coded result B and themean value is compared with a constant δ as a threshold, therebyproducing a signal C. The reason of using the G signal here is in thatof the three R., G and B signals, the G signal is closest to an NDimage.

[0122] First, the input G data are delayed and held by using memories271-1, 271-2, 271-3 and 271-4 on a line by line basis, and the data offive pixels thus successively delayed are added in an adder 272. Theadded value for every pixels is applied to flip-flops (F/F's) 73 to besuccessively delayed and held on a pixel by pixel basis, and theresulting five added values are further added in an adder 275. An outputof the adder 275 is an integral value of 25 pixels adjacent the pixel ofinterest on assumption that the data resulted from delaying the inputdata by 2 lines through memories 271-1, 271-2 and then delaying thedelayed data by 2 pixels through F/F's 273-5, 275-6 is a position of thepixel of interest. Then, the result m obtained by dividing the integralvalue by 25 is used as a threshold for comparison with the data of thepixel of interest in a comparator 279, to thereby provide a binary dataB.

[0123] Thus: $\left\{ {\begin{matrix}{{{{If}\quad G} < m},{{{then}\quad B} = {1\quad ({black})}}} \\{{{{If}\quad G} \geqq m},{{{then}\quad B} = {0\quad ({white})}}}\end{matrix}\quad} \right.$

[0124] On the other hand, both the data are subtracted from each otherin an adder 277 and converted into an absolute value by an absolutevalue circuit 278. Then, the absolute value is compared with theconstant δ in a comparator 274 to obtain a 1-bit signal C indicating adegree of change in the image density.

[0125] Thus:

[0126] If |G−m|>δ, then C=1

[0127] If |G−m|≦δ, then C=0

[0128] In this embodiment, the constant δ is set to be about 20. Therewill now be explained in detail the black character discrimination unit208 based on the black judgment signal d and the binary signals B and C.Note that while the G signal is used in this embodiment, the similarresult can be also obtained by using either one of the remaining R, Bsignals.

[0129] <Black Character Discrimination Unit 208>

[0130]FIG. 16 shows a circuit example of the black characterdiscrimination unit 208. The binary data B binary-coded throughcomparison with the mean value are successively delayed and held byusing line memories 280-1, 280-2, 280-3, and 280-4 on a line by linebasis, and also successively delayed and held by F/F's 281-2 to 281-9 ona pixel by pixel basis. A gate circuit 283-1 receives the input data andoutputs of F/F's 281-0, 281-1, an output of the memory 280-1 and F/F's281-2, 281-3, as well as an output of the memory 280-2 and F/F's 281-4,281-5, that is, binary data of (3×3=)9 pixels about the output positionof the F/F 281-2. Then, the gate circuit 283-1 assigns a value S rangingfrom 0 to 4, which indicates a degree of dot isolation, to the centralpixel, i.e., the output position of the F/F 281-2, based on thesurrounding data.

[0131] Gate circuits (described later) 283-2, 283-4 are, like the abovegate circuit 283-1, to assign the value S ranging from 0 to 4 to theoutput positions of the F/F's 281-4 and 281-6, respectively. The valuesS of 3 pixels in the direction of line are added in an adder 285-1, andthe added value is successively delayed and held over six pixels byF/F's 284-1 to 284-6 while being shifted on a pixel by pixel basis.Then, the respective added values are integrated by an adder 285-2 toobtain a feature amount Pf which is an integral value of S for (3×7=)21pixels adjacent the pixel of interest on the assumption that the outputposition of an F/F 289-4 delayed from the input B data by 2 linesthrough the memories 280-1, 280-2 and then 4 pixels through F/F's 281-4,281-5, 289-3, 289-4 gives a position of the pixel of interest. It can besaid that this feature amount Pf nearly indicates the nature of a screenimage.

[0132] Accordingly, the judgment of black characters is made based onthe following conditions: $\begin{matrix}\left. \begin{matrix}{\quad {{{Pf} < K},}} \\{\quad {B = {1\quad \left( {{recording}\quad {dot}} \right)}}} \\{\quad {C = 1}} \\{\quad {d = {0\quad ({black})}}}\end{matrix} \right\} & (2)\end{matrix}$

[0133] More specifically, the pixel of interest is judged as a part ofblack characters when meeting the above four conditions; the value Pf issmaller than a preset constant K, the binary signal B is at “1” whichmeans recording of a dot, the binary signal C is also at “1” (C=1)meaning that the image itself has a change in density, and the blackjudgment signal d is at “0” (d=0) meaning that the result of colorjudgment is black. In FIG. 16, a comparator 286 compares the constant Kand the feature amount Pf. Then, the binary signal C is synchronizedwith the position of the pixel of interest by being delayed through linememories 280-5, 280-6 and F/F's 282-1, 282-2, 282-3 and 282-4, andinputted to an AND gate 287 along with the outputs of the comparator 286and the F/F 289-4, thereby producing the result of black characterjudgment.

[0134] Details of the arithmetic unit (gate circuit) 283 for Sindicating a degree of isolation is similar to FIG. 5 and thus will notbe explained here. Respective positions of 9 pixels inputted to the gatecircuit 283 are indicated as a to h in FIG. 5 with the pixel of interest(the pixel to be assigned with S) indicated as i. Basically, the valueof S depends on the judgment as to whether or not the level of i isinverted in four directions about i. Specifically, when the level of iis inverted in all the four directions (i.e., i=1 (0) and all a to h=0(1)), S=4 is assigned. When inverted in the three directions, S=3 isassigned. Likewise, When inverted in the n directions, S=n is assigned.

[0135] An output E of the AND gate 287 obtained in FIG. 16 is inputtedto the black character signal generation unit 288 along with dataresulted from delaying the output E by line memories 280-7, 280-8 on aline by line basis, thereby producing final outputs KB, KW. Theconfiguration of the black character signal generation unit 288 issimilar to that shown in FIG. 6.

[0136] From the foregoing process, there can be obtained the signal KBindicating a black character image portion and the adjacent positionsignal KW. The record signal control unit 204 for controlling the recordsignal based on the signals KB, KW of 2 bits will be next explained indetail.

[0137] <Record Signal Control Unit 204>

[0138] The configuration of the record signal control unit 204 issimilar to that shown in FIG. 8. In FIG. 8, the memories 91, 92, 93 and94 are delay memories for matching in position between the C, M, Y and Ksignals and the black character signals KW, Kb, and the synchronizeddata are converted using the ROM's 95, 96, 97 and 98. In the drawing,the ROM 98 is one for controlling the black K signal to provide anenhancement toward a black level (255) in the case of KB=1, as shown.

[0139] On the other hand, the ROM's 95, 96, 97 are ones for convertingthe C, Y and M signals depending on the signals KB, KW of 2 bits suchthat the record data are suppressed as given by CC=½C, for example,toward a white level (0) in the case of KW=1, and further suppressed asgiven by CC=¼C in the case of KB=1. As a special case, it is alsopossible to set CK=255 for the K signal regardless of the input data andset CC=CM=CY=0 for the C, Y and M signals in the case of KB=1 or KW=1,thereby recording black characters by a single color in black and thesurroundings at a higher level in white. Furthermore, in the case ofKB=1, CK may be produced by enhancing the C or M signal, for example,rather than being produced by enhancing the K signal.

[0140] The reason why the respective signals are controlled by using notonly the result of black character discrimination for the pixel ofinterest, but also the discrimination result for those ones surroundingthe pixel of interest as stated above, is in that if an error occurs inthe judgment for the pixel of interest, the resulting image qualitycould be prevented from degrading due to the erroneous judgment.

[0141] <Record Apparatus 205>

[0142] The construction of the record apparatus 205 in FIG. 13 issimilar to that shown in FIGS. 10 to 12.

[0143] This embodiment of the invention is applicable to variousrecording techniques such as ink jet recording, thermal transferrecording, electrostatic recording and electrophotographic recording.

[0144] <Modification (1) of Second Embodiment>

[0145] While in the above second embodiment the black character signalis generated by using the black judgment signal d as the result ofcharacter judgment in FIG. 16, the similar result can be also obtainedby taking the logical product (AND) of the black judgment signal d andthe binary-coded result, and processing a resultant black binary data Bwith the black character judgment algorithm like the above one, tothereby generate the black character signal, as shown in FIG. 17. Inthis embodiment, the black character judgment unit 208 is substantiallythe same as the unit 8 shown in FIG. 4 except that the black judgmentresult d is not applied to the AND gate 87 in FIG. 16. This embodimenthas the advantage that since the black judgment result d is used in thebinarization unit, the delay memory 263 in FIG. 14 can be cut down byabout 2 lines as compared with the above second embodiment.

[0146] <Modification (2) of Second Embodiment>

[0147]FIG. 18 shows another modification in which the black judgmentresult d is reflected on the G data inputted to the binarization unit.The black judgment result d and the G data are inputted to OR gates270-1 to 270-8 on a bit by bit basis so that, only when the blackjudgment result d is “0”, i.e., only in the case of a black pixel, the Gdata are inputted to the binarization unit, followed by execution ofsimilar processing to the above. When the black judgment result d is“1”, i.e., in the case of a colored pixel, all the bits of outputs fromthe OR gates 270 become “1”. In other words, all the outputs representthe data 255 (white), with the result that the G signal suppressed in acolor tint can be generated.

[0148] Specifically, since colored images exclusively exhibit the data255, the difference between the mean value and the pixel data ofinterest becomes zero in those image areas, and the output of thecomparator 274 is always “0”. Eventually, the similar processing to theabove embodiments can be performed by using the black character judgmentunit shown in FIG. 4. This modification (2) of the second embodiment hasthe advantage that since the color judgment result d is not required tobe delayed, the delay memory 263 in FIG. 14 can be omitted.

[0149] As described above, the present invention represented by thesecond embodiment comprises means for judging a specific color from aplurality of color component signals, means for extracting a line imageportion from at least one color signal among the plurality of colorcomponent signals, means for discriminating the line image portion ofthe specific color based on an output of the extraction means and thejudgment result of the judgment means, and means for controlling recordcolor signals for a pixel of interest depending on discriminationresults of the pixel of interest and surrounding pixels from thediscrimination means, thereby providing advantages below:

[0150] (1) Black characters and lines in a color image can bediscriminated inexpensively with high accuracy, enabling characters tobe recorded by the use of a single black color with high resolution,

[0151] (2) Even if a color shear is caused during the recording, blackcharacters can be clearly recorded in black, and

[0152] (3) Particularly, according to this embodiment, since the recordcolor signals for the pixel of interest are controlled depending on thediscrimination results of the pixel of interest and the surroundingpixels in relation to the line image portion, higher-accurate controlcan be achieved as compared with the case of making control based on thepixel of interest alone.

[0153] As printers to output the record signals generated in anabove-stated manner, there can be used such printers capable of colorrecording as a color ink jet printer, a color thermal transfer printer,a color dot printer and a color laser beam printer.

[0154] In particular, the present invention represented by the secondembodiment is also effective for use in a printer having a head of thetype that droplets are discharged by utilization of film boiling underthermal energy, as disclosed in U.S. Pat. Nos. 4,723,129 and 4,740,793.

[0155] The aforementioned arithmetic circuits may be constituted usingROM's, RAM's or the like, or may be realized by a software executed in acomputer to implement the above arithmetic operations.

[0156] Other than being applied from the CCD sensor, the image data maybe applied from a host computer through an interface, or from anexternal storage unit.

[0157] The specific color is not limited to black and may be blue orred.

[0158] How to obtain the discrimination result of the surrounding pixelsis not limited to the illustrated embodiment, and the discriminationresult may be derived from information of 5×5 or 7×7 matrix, forexample.

[0159] In addition, other than operating the logical sum (OR), thesignal KW may be generated by, for example, counting the number of thosepixels which are judged as belonging to black characters from thediscrimination results, and setting some threshold as a slice level.

[0160] According to the second embodiment of the present invention, asexplained above, black lines in a color image can be satisfactorilyreproduced.

[0161] [Third Embodiment]

[0162]FIG. 19 shows an entire block diagram of a third embodiment of thepresent invention. In the drawing, designated by reference numeral 301is an image input unit comprising a CCD line sensor for R, G and B.Analog image signals subjected to color separation into r, g and b onpixel by pixel basis are quantized by an A/D conversion unit 302 intodigital image signals R, G and B each having an 8-bit (0 to 255) width.The quantized data are converted through log conversion made by a dataconversion unit 303, here not explained in detail, into image signals ofY, M and C as record colors. The data conversion unit 303 generallycarries out well-known data conversion such as correction of unevennessoccurred in the image reading unit including the sensor 301, logconversion, so-called masking processing dependent on spectroscopiccharacteristics of the sensor 301 and recording material, enlargementand reduction of size, etc.

[0163] Error correction units 304, re-quantization units 306, andmemories 307, 305, all designed to make processing for each color of Y,M and C, jointly constitute the so-called pseudo-half-tone processingunit for re-quantizing Y, M and C record signals, each having an 8-bitwidth, into y, m and c signals each of which has the lesser number ofbits. The re-quantized y, m and c signals are inputted to a black signalgeneration unit 309 for newly generating a black record signal K andalso correcting the inputted y, m and c signals into y′, m′ and c′signals to be actually used as record data. Then, a record apparatus 310forms a visual image.

[0164] A third embodiment of the present invention adapted to make thepseudo-half-tone processing into binary data will now be described withreference to FIG. 20. The pseudo-half-tone processing technique used inthis embodiment is one already proposed by the applicant, theconfiguration of which is mainly divided into a memory 307 for delayingand holding the binary data by 2 lines which have been alreadybinary-coded, a binarization unit 360 for holding the binary dataoutputted on a pixel by pixel basis from the memory 307 in units of 12pixels adjacent the pixel of interest, determining a binary thresholdfrom those 12 binary data for binarization, and producing a binarizationerror, an error memory 305 for delaying and holding the error by 1 line,and an error correction unit 304 for correcting the input image signalbased on the error.

[0165] <Binarization Unit 360>

[0166] Details of the binarization unit 360 will be explained withreference to FIGS. 21 and 22. In FIG. 21, F/F's 605 and 601 respectivelyreceive the binary data of preceding 1 line and 2 lines from the line ofinterest which is delayed and held by the memory 307. In response to thedata clock (not shown), the received binary data are successivelydelayed and held on a pixel by pixel basis by F/F's 602, 603, 604 andF/F's 606, 607, 608. On the other hand, an output of an F/F 610 whichreceives the result of binarizing the pixel of interest is also delayedand held by an F/F 609. Letting input and output signals of therespective flip-flops be designated by a-k as illustrated, there areobtained 12 data which have been already binary-coded andtwo-dimensionally adjacent the position * of the pixel of interest asshown in FIG. 22.

[0167] In FIG. 21, a mean value calculation ROM 614 having input addressterminals, to which the above 12 binary data are connected, is a ROM formultiplying the pixels at the positions a-j by weighting factors to beapplied to the binary data at the positions a-j with respect to thepixel of interest, as shown in FIG. 22, for conversion into a weightedmean value. This weighted mean value outputted from the ROM 614 becomesa threshold for binarizing the pixel of interest. A comparator 612serves to binary-code the input data of which error has been correctedby the error correction unit (described later). The binary-coded resultis inputted to both the memory 307 and the F/F 610 for binarization of anext pixel. Meanwhile, the output of the mean value calculation ROM 614is also applied to a subtracter 611 to determine the difference betweenthe mean value and the input data after error correction. An output ofthe subtracter 611 gives an binarization error specific to the presentpseudo-half-tone processing technique unlike the well-known errordispersing technique. The binarization error is divided into two equalparts by an alloter 613, following which one half e2 is inputted to theerror memory 305 for correction of next line pixel data and the otherhalf e1 is inputted to the error correction unit 304 for correction ofnext pixel data.

[0168] <Error Correction Unit 304>

[0169] The error correction unit 304 is shown in FIG. 23. The input8-bit image data is added in an adder 342 with both the binarizationerror e1 occurred during binarization of the last pixel and thebinarization error e2 outputted from the error memory 305, i.e.,occurred during binarization of the pixel of preceding 1 line. The inputdata after error correction is applied to an F/F 341 and, in response tothe next clock, then applied to the subtracter 611 and the comparator612, followed by execution of the binarization processing similar to theabove.

[0170] The above binarization processing is executed in parallel for thethree color data of C, M and Y independently of each other in a likemanner, thereby obtaining the binary data y′, m′ and c′.

[0171] <Generation of Black Signal>

[0172] An output of an AND gate 309K receiving the y′, m′ and c′ signalsgives a black signal k to be recorded. Outputs of AND gates 9Y, 9M and9C respectively receiving the black signal k and the y′, m′ and c′signal give the y, m and c signals as record color signals.

[0173] That process will now be explained by referring to a YMC colorspace shown in FIG. 24. Assuming that the binary-coded threshold (meanvalue) resulted from those of every pixels in the YMC space is M, thespace is divided into eight parts in the directions of three YMC axes.Now, if the input data after error correction is present at a positionP, the binary-coded results of the three colors all become “1”.Therefore, the black to be otherwise recorded by three colors isreplaced with only one color K which can be expressed using an ⅓ amountof recording material. Eventually, the recording can be made byrecording materials of two colors at maximum. In other words, it ispossible to use seven colors of Y, M, C, K, Y+M, M+C and C+Y as recordcolors per pixel.

[0174] A modification of the black signal generation unit 309 in thethird embodiment will be next explained.

[0175] <Modification (1) of Black Signal Generation Unit>

[0176]FIG. 25 shows a modification of the black signal generation unit.In FIG. 25, designated by 391 is a min value detection unit forreceiving the Y, M and C data and determining the minimum value amongthem. The resulting minimum value is compared in a comparator 392 with acertain constant α preset by a CPU (not shown). If the minimum value islarger than α, then a level “1” is outputted to an AND gate 390.Specifically, because the minimum value of the Y, M and C signalsindicates brightness of the input pixel, some level of brightness, i.e.,the case of the minimum value being smaller than α, implies that recorddots are not so dense in the vicinity of the pixel of interest. Thus,there is no need of displacement with only one color of the K signal. Onthe contrary, it is possible to prevent the obtrusive texture whichwould be caused by the replaced K dots.

[0177] In addition, the similar advantage can be also obtained by usingthe mean value of Y, M and C, for example, other than the minimum value.

[0178] <Modification (2) of Black Signal Generation Unit>

[0179] While blackish portions in the input image are replaced withnearly only one K color in the above embodiment and modification, therecord image can exhibit deepness by adding dots of other one color tothe K color. In a modification shown in FIG. 26, when a comparator 393detects the presence of the minimum value smaller than a preset value β(which is larger than α), a max value detection unit 394 detects thecolor having a maximum value. In this case, the black is expressed byusing total two colors; i.e., the K color and the color of the maximumvalue. More specifically, in the case of c′, m′ and y′ being all “1” atthe AND gate 390, when the comparator 393 detects the minimum valueexceeding β, an AND gate 396 produces an output of “1”, while the maxvalue detection unit 394 produces an output of “1” in only the color ofthe maximum value. As a result, one of AND gates 397 cmy produces anoutput of “1”, allowing a dot to be recorded in one color+the K color.

[0180] The color for use in recording in addition to black is notlimited to the color of the maximum value and may be the color of theminimum value or one fixed color such as magenta or cyan. Particularly,in the case of using cyan, even if there occurs a shear between blackand cyan dots, the shear can be less visually recognized. From thisstandpoint, cyan is superior to magenta.

[0181] Furthermore, instead of using other one color in addition toblack, the black may be used twice in superposed relation. Thisalternative is advantageous in that since there is no problem of a colorshear, dots are not always required to superpose therebetween at thesame position.

[0182] The above method of superposing multiple dots enables blackcharacters to be expressed more clearly, and is effective in,particularly, ink jet printer or the like in which the specific densityof black ink on recording paper cannot be increased beyond a certainlevel.

[0183] <Modification (3) of Black Signal Generation Unit>

[0184] By combining the modifications (1) and (2) with each other, therecording can be made with higher quality. More specifically, as shownin FIG. 27, the black signal generation unit of this modification isdesigned to meet the following relationships of Table 2 when c′, m′ andy′ are all at “1”. TABLE 2 Conditions c m y k min (Y,M,C) < α 1 1 1 0 α< min (Y,M,C) < β 0 0 0 1 min (Y,M,C) > β (only color of 1 max (Y,M,C)1)

[0185] By so setting, it is possible to make the recording almost in twocolors.

[0186] Note that the pseudo-half-tone processing used is not limited tothe illustrated embodiment, the similar advantage to this embodiment ofthe present invention can be also obtained by employing the errordispersing technique or the like.

[0187] An edge may further be extracted in addition to detection of thecolor of the maximum value. More specifically, as shown in FIG. 28, awell-known edge extraction unit 399 may be provided to inhibit therecording in two colors when an edge is detected depending on a 1-bitjudgment signal (1 indicating the presence of edge, 0 indicating theabsence of edge). This enables it to prevent a color shear which mayoccur at edges.

[0188] <Record Apparatus 310>

[0189] The construction of the record apparatus 310 in FIG. 19 issimilar to that shown in FIGS. 10 to 12.

[0190] This embodiment of the invention is applicable to variousrecording techniques such as ink jet recording, thermal transferrecording, electrostatic recording and electrophotographic recording.

[0191] With this embodiment, the RGB input image data arecolor-separated into three record colors of C, M and Y, the resultingimage data in three colors are independently subjected to thepseudo-half-tone processing for re-quantization, and record data in fourcolors of c, m, y and k are produced based on the re-quantized data,making it possible to control the amounts of all kinds of recordingmaterials to be recorded on one point over the surface of recordingpaper.

[0192] In other words:

[0193] (1) The number of color dots to be recorded on one point over thesurface of recording paper can be limited nearly to two colors among thefour colors of C, M, Y and K, with the result of high-quality recording.

[0194] (2) As compared with the case of independently producing the Ksignal by the use of masking and UCR for binarization, the binarizationcircuit in one color can be dispensed with and the apparatus can be thusrealized inexpensively.

[0195] This embodiment of the invention comprises means for making aplurality of color component signals subjected to pseudo-half-toneprocessing color by color for binarization, means for removing minorcolor components from the color component signals, and means forgenerating record color signals by using both the color component signalleft after removing the minor color components and the color componentsignals before the binarization, thereby improving color reproducibilityof black line image portions, in particular.

[0196] As printers to output the record signals generated in anabove-stated manner, there can be used such printers capable of colorrecording as a color ink jet printer, a color thermal transfer printer,a color dot printer and a color laser beam printer.

[0197] In particular, the present invention represented by the secondembodiment is also effective for use in a printer having a head of thetype that droplets are discharged by utilization of film boiling underthermal energy, as disclosed in U.S. Pat. Nos. 4,723,129 and 4,740,793.

[0198] The aforementioned arithmetic circuits may be constituted usingROM's, RAM's or the like, or may be realized by a software executed in acomputer to implement the above arithmetic operations.

[0199] Other than being applied from the CCD sensor, the image data maybe applied from a host computer through an interface, or from anexternal storage unit.

[0200] The binarization processing is not limited to that disclosed inthe above embodiment and may be implemented by the error dispersingtechnique or the like pseudo-half-tone processing, or any other suitablebinarization processing.

[0201] In addition, this embodiment is not limited to binarization andinput n bits may be coded into any value ranging from 0 to m (where 2≦m<n).

[0202] According to the third embodiment of the present invention, asexplained above, there can be provided an image processing apparatuswhich has satisfactory reproducibility of colors.

[0203] The present invention is not restricted to the embodimentsexplained above, and various modifications and applications can be madewithout departing from the scope of the attached claims.

What is claimed is:
 1. An image processing apparatus comprising: a)first judgment means for judging whether or not a pixel of interestbelongs to a black line image portion, and outputting a first judgmentsignal indicating a judgment result, b) second judgment means forjudging whether or not pixels in the vicinity of said pixel of interestbelong to a black line image portion, and outputting a second judgmentsignal indicating a judgment result, and c) control means forcontrolling recording of said pixel of interest based on the first andsecond judgment signals outputted from said first and second judgmentmeans.
 2. An image processing apparatus according to claim 1, whereinsaid first and second judgment means make judgment using data of thosepixels surrounding said pixel of interest.
 3. An image processingapparatus according to claim 1, wherein said control means controls tomake recording by using only black, when said first judgment meansjudges that said pixel of interest belongs to a black line imageportion.
 4. An image processing apparatus according to claim 1, whereinsaid control means control to make recording by using no record colorsother than black, when said second judgment means judges that pixels inthe vicinity of said pixel of interest belong to a black line imageportion.
 5. An image processing apparatus according to claim 1, furthercomprising image forming means which performs image forming undercontrol by said control means.
 6. An image processing apparatusaccording to claim 5, wherein said image forming means includes a headof the type that liquid droplets are discharged by utilization of filmboiling with thermal energy.
 7. An image processing method comprising:a) a first judgment step of judging whether or not a pixel of interestbelongs to a black line image portion, b) a second judgment step ofjudging whether or not pixels in the vicinity of said pixel of interestbelong to a black line image portion, and c) a control step ofcontrolling recording of said pixel of interest based on judgmentresults in said first and second judgment steps.
 8. An image processingmethod according to claim 7, wherein in said first and second judgmentsteps, the judgment is made using data of those pixels surrounding saidpixel of interest.
 9. An image processing method according to claim 7,wherein in said control step, control is performed to make recording byusing only black when said first judgment step judges that said pixel ofinterest belongs to a black line image portion.
 10. An image processingmethod according to claim 7, wherein in said control step, control isperformed to make recording by using no record colors other than blackwhen said second judgment step judges that pixels in the vicinity ofsaid pixel of interest belong to a black line image portion.
 11. Animage processing method according to claim 7, further comprising a stepof forming an image under control by said control step.
 12. An imageprocessing method according to claim 11, wherein said image forming isperformed by using a head of the type that liquid droplets aredischarged by utilization of film boiling with thermal energy.
 13. Animage processing apparatus comprising: a) m-value coding means forcoding a plurality of color component signals, each in n bits, one byone into any value ranging from 0 to m (where 2≦m<n), b) judgment meansfor judging whether or not an image represented by said plurality ofcolor component signals belongs to a black line image portion, and c)control means for controlling, based on a judgment result by saidjudgment means, recording with a plurality of color component signalswhich have been coded by said m-value coding means into any valueranging 0 to m.
 14. An image processing apparatus according to claim 13,wherein said m-value coding means performs the coding into any valueranging from 0 to m in consideration of an error in quantization.
 15. Animage processing apparatus according to claim 13, wherein said colorcomponent signals are color component signals of yellow, magenta andcyan.
 16. An image processing apparatus according to claim 13, furthercomprising image forming means which performs image forming undercontrol by said control means.
 17. An image processing apparatusaccording to claim 16, wherein said image forming means includes a headof the type that liquid droplets are discharged by utilization of filmboiling with thermal energy.
 18. An image processing apparatuscomprising: a) means for judging a specific color from a plurality ofcolor component signals, b) means for extracting a line image portionfrom at least one color signal among said plurality of color componentsignals, c) means for discriminating the line image portion of saidspecific color based on an output of said extraction means and ajudgment result of said judgment means, and d) means for controllingrecord color signals for a pixel of interest depending on discriminationresults of the pixel of interest and surrounding pixels from thediscrimination means,
 19. An image processing apparatus according toclaim 18, wherein said specific color is black.
 20. An image processingapparatus according to claim 18, further comprising image forming meanswhich performs image forming under control by said control means.
 21. Animage processing apparatus according to claim 20, wherein said imageforming means includes a head of the type that liquid droplets aredischarged by utilization of film boiling with thermal energy.
 22. Animage processing apparatus comprising: a) means for binary-coding aplurality of color component signals color by color, b) means forremoving minor color components from said color component signals, andc) means for generating record color signals by using both the colorcomponent signal left after removing said minor color components andsaid color component signals before the binary-coding.
 23. An imageprocessing apparatus according to claim 22, wherein said binary-codingmeans performs the binary-coding with pseudo-half-tone processing. 24.An image processing apparatus according to claim 22, wherein saidbinary-coding means performs the binary-coding in consideration of anerror in quantization.
 25. An image processing apparatus according toclaim 22, further comprising image forming means which performs imageforming based on said record color signals generated by said generatingmeans.
 26. An image processing apparatus according to claim 25, whereinsaid image forming means includes a head of the type that liquiddroplets are discharged by utilization of film boiling with thermalenergy.
 27. An image processing apparatus comprising: a) detecting meansfor detecting a black line image portion in an input color image, and b)generating means for generating record signals to record the black lineimage portion, detected by said detecting means, by superposing multipledots including a black dot.
 28. An image processing apparatus accordingto claim 27, wherein said detecting means detects by using data ofpixels in the vicinity of a pixel of interest.
 29. An image processingapparatus according to claim 27, wherein said multiple dots comprise atleast a black dot and another color dot.
 30. An image processingapparatus according to claim 29, wherein said another color dot is a dotof the color component having a maximum value among a plurality of colorcomponent signals which represent said input color image.
 31. An imageprocessing apparatus according to claim 27, further comprising imageforming means which performs image forming based on said record signalsgenerated by said generating means.
 32. An image processing apparatusaccording to claim 31, wherein said image forming means includes a headof the type that liquid droplets are discharged by utilization of filmboiling with thermal energy.
 33. An image processing method comprisingthe steps of: a) detecting a black line image portion in an input colorimage, and b) generating record signals to record said black line imageportion by superposing multiple dots including a black dot.
 34. An imageprocessing method according to claim 33, wherein said multiple dotscomprise at least a black dot and another color dot.
 35. An imageprocessing method according to claim 34, wherein said another color dotis a dot of the color component having a maximum value among a pluralityof color component signals which represent said input color image. 36.An image processing method according to claim 33, further comprising animage forming step to perform image forming based on said record signalsgenerated by said generating step.
 37. An image processing apparatusaccording to claim 36, wherein said image forming is performed by usinga head of the type that liquid droplets are discharged by utilization offilm boiling with thermal energy.